1. Field of the Invention
The present invention relates to a portable timepiece in which there is a possibility of the inner pressure of the timepiece exterior assembly being enhanced, for example, as in the case of a diver's watch for saturation diving and the like.
2. Background Information
There is known a diver's watch for saturation diving in which, to cope with a case in which the inner pressure of the case has become higher than the outer pressure, an automatic degassing valve provided in the case is operated, making it possible to automatically discharge the gas inside the case to the exterior of the case (See, for example, JP-A-2003-240877 Patent Document 1).
The automatic degassing valve with which the diver's watch is equipped has a stepped hole extending through the case, a pipe, a valve, a coil spring, and waterproof packing.
More specifically, a small diameter hole portion of the stepped hole is open to the inner side of the case, and a large diameter hole portion of the stepped hole is open to the outer side of the case. The pipe has a step portion, and is inserted into the small diameter hole portion from the large diameter hole portion, with positioning being effected thereon at the step formed by the small diameter hole portion and the large diameter hole portion. At least a part of the valve is inserted into the interior of the pipe so as to be axially movable, and this valve has a head portion situated on the large diameter hole portion side, and a receiving portion situated in the small diameter hole portion. The coil spring is held in a compressed state between the step portion and the receiving portion, urging the valve toward the inner side of the case. The waterproof packing is provided so as to be compressed between the pipe portion overlapping the step of the stepped hole and the head portion of the valve by the urging force of the coil spring.
When the inner pressure of the case is lower than the urging force of the coil spring, this automatic degassing valve is maintained in the closed state. However, the inner pressure of the case is enhanced by the helium gas entering the case with the saturation diving operation, so that, under the atmospheric pressure, the valve is moved toward the outer side of the case against the urging force of the coil spring, whereby the compression of the waterproof packing is released. In this way, the automatic degassing valve is opened, so that the gas in the case is discharged. As a result, there is no difference in pressure between the interior and exterior of the case; then, the automatic degassing valve is placed in the closed state again by the urging force of the coil spring.
In a residential area of a helium gas atmosphere installed under water, the helium gas in this residential area is transmitted through the waterproof packing of the automatic degassing valve with which the diver's valve of Patent Document 1 is equipped, and enters the case of the diver's watch. In this case, in addition to the fact that only one waterproof packing is used, the waterproof performance due to this waterproof packing mainly depends on the coil spring; however, the urging force of the coil spring compressing the waterproof packing involves relatively large variation from spring to spring. Thus, in the diver's watch of Patent Document 1, it is highly possible that the helium gas used in saturation diving being transmitted through the waterproof enters the case, and the inner pressure of this case is likely to be enhanced.
Further, in a situation in which the automatic degassing valve is opened after saturation diving, there is a possibility of water being accumulated in the large diameter hole portion of the stepped hole, and, under rainy weather, rain water may enter the large diameter hole portion. When degassing is automatically performed in such a situation, there may be a fear of the water in the large diameter hole portion entering the case immediately after the completion of exhaust and in a state in which the waterproof packing is not compressed.
As described above, in the prior art technique, gas is likely to be transmitted from the outside into the case via the automatic degassing valve, and there is a fear of water being allowed to enter from the outside with the completion of the degassing operation.